Add CPPFLAGS so this can be cross-compiled.

dist/bind/bin/probe_ipv6

@@ -1,6 +1,6 @@
 #!/bin/sh
 #
-#	$NetBSD: probe_ipv6,v 1.2 1999/11/20 19:03:47 veego Exp $
+#	$NetBSD: probe_ipv6,v 1.3 1999/12/24 19:11:25 garbled Exp $
 
 set -e
 PATH=/bin:/usr/bin:$PATH; export PATH
@@ -30,10 +30,10 @@ cat > ${new} <<EOF
 
 EOF
 
-if ${CC} -c tmp$$a.c > /dev/null 2>&1
+if ${CC} ${CPPFLAGS} -c tmp$$a.c > /dev/null 2>&1
 then
         echo "#define HAS_INET6_STRUCTS" >> ${new}
-        if ${CC} -c tmp$$b.c > /dev/null 2>&1
+        if ${CC} ${CPPFLAGS} -c tmp$$b.c > /dev/null 2>&1
         then
 		:
 	else